However, adding the blood thinner Lovenox (enoxaparin) to the mix does not reduce their chances of dying from a blood clot, according to research appearing in the Dec. 29 issue of the New England Journal of Medicine.

In the new study, almost 4,200 patients received Lovenox plus compression hose and more than 4,100 were given compression hose plus a placebo to lower their risk of developing a deep venous thrombosis (DVT). These blood clots tend to occur in the lower leg and thigh, where they can block blood flow and cause swelling and pain. If a clot dislodges -- becoming an embolism -- it can travel to the lungs or brain, resulting in organ damage and even death.

After 30 days of treatment, the rate of dying was similar between both groups of patients. Among those individuals who were given Lovenox, the risk of death from any cause was 4.9 percent. By contrast, this risk was 4.8 percent among those participants who were given a placebo. The risk of major bleeds was similar between both groups as well. The new study was supported by Sanofi, which manufactures Lovenox.

"Does the use of Lovenox affect all-cause mortality? The answer in our study is no. We were unable to demonstrate benefit," said study author Dr. Ajay Kakkar, of the Thrombosis Research Institute and the University College London Hospitals NHS Foundation Trust, in England.

In addition to keeping these patients alive, doctors aim to prevent "the development of blood clots and the long-term consequences of these blood clots," Kakkar said. "You could look to other potential benefits, but we can't say a blood thinner will prevent death from blood clots in this group of patients."

Exactly why this agent did not help lower risk of DVT-related death is unclear. These patients may have been too ill, and blood clots may not be as common a cause of death as previously believed. "There are so many other bad things that are happening that might ultimately be the cause of their death," he said. "Preventing fatal blood clots, although important, may be an infrequent cause of death."

In this study, "a patient's risk of dying from a blood clot was the same whether they had compression stockings alone or compression stockings plus Lovenox," said Dr. Robert Myerburg, a cardiology professor at the University of Miami School of Medicine. "These are patients with serious medical conditions, not post-surgical patients." The new findings do not apply to people who take blood thinners after surgery to stave off blood clots.

Myerburg said the findings will not change how he treats his severely ill patients and there are other reasons to prescribe blood thinners in this group. "They may be getting other benefits from the medication that don't translate into a lower mortality risk, including the prevention of blood clots and their other consequences."

SOURCES: Ajay Kakkar, MB, BS, Ph.D., Thrombosis Research Institute, London and University College London Hospitals NHS Foundation Trust; Robert Myerburg, M.D., cardiology professor, University of Miami School of Medicine; Dec. 29, 2011, New England Journal of Medicine